1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly to a method of fabricating a high-performance bipolar transistor by the use of laser irradiation.
2. Description of the Prior Art
As is well known, in order to obtain a high performance bipolar transistor, it is required to make small the depth of he emitter junction and to make the carrier injection from the side face of the emitter in the lateral direction as little as possible.
To fulfill these requirements, there has been proposed a method in which, as is shown in FIG. 1 of the accompanying drawings, a principal surface of a semiconductor substrate 1 is coated with an insulating film 2, that part of the insulating film 2 where an emitter is to be formed, is removed to expose the surface of the semiconductor substrate 1, and a semiconductor film 3 is epitaxially grown on the exposed surface of the substrate 1 to form an emitter. Incidentally, reference numerals 5 and 6 in FIG. 1 designate a base and a collector, respectively.
Such an emitter, namely, an emitter formed on a substrate is called "a stacked emitter". Since the stacked emitter is formed on a substrate and moreover the side faces of the emitter are kept in contact with an insulating film, a transistor with a stacked emitter has an advantage such that the carrier injection in the lateral direction scarcely takes place and therefore high frequency characteristics are greatly improved.
However, since a conventional stacked emitter has been formed by epitaxial growth, a prior art method of forming the stacked emitter necessitates a complicated process, is required to strictly meet various process conditions, and therefore is low in productivity. Further, the prior art method has such a drawback that an epitaxial layer, as shown in FIG. 1, is apt to grow obliquely at that end portion thereof which is kept in contact with the insulating film 2, thereby forming a facet 4 thereat to lower reliability.